[v2] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop.

[Michael Ellerman]

On Wed, 2018-07-18 at 08:33:16 UTC, "Gautham R. Shenoy" wrote:
> From: "Gautham R. Shenoy" <ego at linux.vnet.ibm.com>
> 
> On 64-bit servers, SPRN_SPRG3 and its userspace read-only mirror
> SPRN_USPRG3 are used as userspace VDSO write and read registers
> respectively.
> 
> SPRN_SPRG3 is lost when we enter stop4 and above, and is currently not
> restored.  As a result, any read from SPRN_USPRG3 returns zero on an
> exit from stop4 and above.
> 
> Thus in this situation, on POWER9, any call from sched_getcpu() always
> returns zero, as on powerpc, we call __kernel_getcpu() which relies
> upon SPRN_USPRG3 to report the CPU and NUMA node information.
> 
> Fix this by restoring SPRN_SPRG3 on wake up from a deep stop state
> with the sprg_vdso value that is cached in PACA.
> 
> Fixes: e1c1cfed5432 ("powerpc/powernv: Save/Restore additional SPRs
> for stop4 cpuidle")
> 
> Reported-by: Florian Weimer <fweimer at redhat.com>
> Cc: <stable at vger.kernel.org> # 4.14
> Cc: Oleg Nesterov <oleg at redhat.com>
> Cc: Michael Neuling <mikey at neuling.org>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Cc: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>
> Signed-off-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/b03897cf318dfc47de33a7ecbc7655

cheers